Buster upgrade procedure

apt-get update
apt-get install -y aptitude
aptitude search '~i(!~ODebian)' # should return as little as possibile
apt-get upgrade
apt-get dist-upgrade
dpkg -C # should return nothing or as little as possibile
apt-mark showhold # should return nothing or as little as possibile
dpkg --audit # should return nothing
cp /etc/apt/sources.list /etc/apt/sources.list_backup
sed -i 's/stretch/buster/g' /etc/apt/sources.list
apt-get update
apt list --upgradable
apt-get upgrade -y
apt-get dist-upgrade -y 
aptitude search '~i(!~ODebian)' # should return same as before
apt-get autoremove

or

apt clean && apt update && apt upgrade
apt full-upgrade
apt --purge autoremove
reboot

cp -v /etc/apt/sources.list /root/apt.src.stretch/
cp -rv /etc/apt/sources.list.d/ /root/apt.src.stretch/
sed -i 's/stretch/buster/g' /etc/apt/sources.list
sed -i 's/stretch/buster/g' /etc/apt/sources.list.d/*
apt update && apt upgrade


apt full-upgrade
reboot

uname -r && lsb_release -a
apt --purge autoremove